Carrier-wave signaling system



2 Sheets-Sheet 1 mm M E; :2 H a; H 5 H I R. A. HEISING CARRIER WAVE SIGNALING SYSTEM Filed Dec. 1, 1924 March 15, 1927.

Wren/07:" ,ayma/rd lfle/J/ky 2/ arch 927 R. A. HEISING CARRIER WAVE SIGNALING SYSTEM Filed Dec. 1, 1924 2 Sheets-Sheet 2 Patented Mar. 15, 1927.

UNITED STATES PATENT OFFICE.

RAYMOND-A. HEISING, OF MILLBURN, NEW JERSEY, ASSIGNOR TO WESTERN ELEG- TRIC COMPANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF NEW 'YORK.

CARRIER-WAVE SIGNALING SYSTEM.

Application filed December 1, 1924. Serial No: 753,029.

includes the combination of an electric discharge oscillator feeding into a power amplifier.

These objects are achieved in one specific embodiment of the invention by using an oversize vacuum tube oscillator coupled with a' power amplifier in the transmitting circuit, the oscillator being of the type in which the input and output circuits are capacitatively coupled. This expedient promotes a constancy of frequency of the oscillator by providing a relatively low impedance shunt path for the potential variations occurring between the grid and filament, for example. of the power amplifier which would otherwise react on the oscillator to the detriment of its normal function of generating a constant frequency. Since the operation of an oversize oscillator, as compared with that of a normal size oscillator is characterized .by the generation of a larger amplitude of current in its output circuit, sufiicient voltage for exciting the grid of the power amplifier can he obtained by using a larger condenser (hence a condenser of smaller impedance) for coupling the oscillator and the amplifier.

Other objects and features of the invention will be apparent from a consideration of the following detailed description taken in connection with the accompanying drawings. inwhich Figs. 1 and 2 illustrate the circuits at the two respective terminal stations of a two-way radio communication system.

In the drawing the various elements of the system are labelled with identifying symbols which are suggestive of the functions of the elements. For example, the lettors \V and E prefixed to the identifying symbols respectively indicate that the elements are used at the west and east termini of the system. Similarly, the letters FB, M, 0, AS, AN, AP, SR, and D are used to indicate respectively, a band filter, a modulator, an oscillator, a speech amplifier, an antenna, a power amplifier, a speech scrambler, and a detector. The labels of elements having similar functions at the two stations are differentiated only by the use of the letters W and E. and elements at the same terminus which have similar functions will be distinguished by the use of different subscripts. Graphical devices adjacent the circuits at various points depict, on 2!. scale of abscissae, the relative ranges occupled by the frequencies of the currents transmitted at these points. Cross hatching between the vertical lines marking out these ranges identifies the portions of the frequency range occupied by signal currents. The vertical wave line hatching indicates the portion of the frequency range occupied by noise currents. It will be assumed that the circuits illustrated in Fig. 1 are at the west terminus and that the circuits illustrated in Fig. 2 are at the eastterminus.

The system comprises a two-way radio communication system for transmitting speech or other low frequency signals between a low frequency line 1 and radio aplar arrangement of low frequency and radio apparatus constituting the terminal equipment of the east station of the system, to or from the east terminus which is similarly provided with transmitting and receiving instruments. Although in Fig. 2 the transmitting and receiving instruments T and R are illustrated as unrelated. they may equally well be connected to a common low frequency line in a manner similar to line 1 at the west terminus. Transmission from west to east occurs through the circuits indicated in the upper halves of Figs. 1 and 2. Transmission from east'to west correspondingly occurs by means of the circuits illustrated in the lower halves of these figures. Although applicable. to any point-to-point system the circuits are illustrated for use in a ship-to-shore radio communication system for which it is especially well adapted the west terminus being the shore station and the east terminus the ship station.

At the west station, since the low frequency circuits used for transmitting and receiving are joined to a common low frequency transmission line, a means must be employed to insure substantial conjugacy of these circuits, so that low frequency transmitted waves will not enter the radio receiving circuits to impair their efliciency for simultaneous or future reception, and so that the received waves will not enter the radio transmitting circuits to set up a singing condition. The triple-wound transformer or hybrid coil 3 and artificial network N are provided for this purpose. The theory and application of hybrid coil arrangements in connection with balancing net works are now well known and do not appear to require further description in this specification.

The circuits for eastward transmission, intermediate the hybrid coil at the west station and the receiver R at the east station are illustrated in some detail. The correspondin in icated diagrammatically since the elements of this circuit are in large part duplicates of the corres nding elements of the eastward transmisslon circuit. The" operation of the circuits for eastward transmission will now be considered in detail.

Voice currents from the low-frequency line 1 pass through the hybrid coil 3, into low frequency line 2. These speech currents will be assumed, for convenience to comprise frequencies between the limits of 200 to 2500 cycles. These currents are divided, one portion flowing through branch circuit 4 and the other through branch circuit 5. The currents flowing in these respective circuits are distinguished by the difierent relative frequency ranges which they occupy. The frequencies of the currents flowing through circuit 4. occupy the ranges from 200 to 800 cycles and from 1500 to 2500 cycles. The currents flowing through branch 5. occupy the rangev from 800 to 1500 cycles. The necessary frequency segregation required to produce this result is accomplished, respectively, b the filter circuits WFB and WFB,-. These filler circuits are respectively designed to pass, without appreciable attenuation, the currents lying within the frequency limits to be transmitted respectively through circuits 4 and 5 and to suppress the currents lying outside these limits. Filters for this purpose may be desi ned in accordance with the disclosure in U. Patents 1,227,113 and 1,227,114, Ma 22, 1917, and 1,493,600, May 13, 1924, to ampbell.

The combination of elements included in branches 4 and 5 constitute what will hereinafter be called a speech scrambler and circuits for transmission westward are that included in branch 5 a speech transposer. The speech sub-bands transmitted through branch 4 are transmitted unchan ed 7 to circuit 6. The speech sub-band traversing branch 5 is transposed to a higher or lower level by combining it in modulator WM with oscillations supplied by the oscillator VVOM. For practical purposes, it is convenient to transpose this sub-band to approximately a position in the frequency spectrum between 2700 and 3400 cycles. The reason for so choosing the frequency range to which the sub-band is transposed will be described later. For this purpose the frequency of the oscillator WO should be 1900 cycles. The sum frequencies of the 'im ressed currents is selected by band pass filter WFB This will result in a transposition of the frequency band with no other change. If the frequency of the oscillator were made 4200 cycles and the difference frequency components, instead of the sum frequency components, were selected b band pass filter WFB there would resu t a similar trausposition and also a com lete inversion of the frequencies in the band.

The step of transposing and invertin frequencies in accordance with the method just described is disclosed in U. S. Patent to Van der Bijl 1,502,889, issued July 29, 1924.

The transposed sub-band transmitted through branch 5 and the unchanged subband traversing branch 4 are supplied. to circuit 6, where, accordingly, they occupy three distinct frequency ranges; one between 200 and 800 cycles, the second between 1500 and 2500 cycles and the third between 2700 and 3400 cycles. This represents greatly distorted speech. Obviously, the transposed sub-band could be made immediately adjacent the second sub-band, or it could be displaced further therefrom but stillwithin the range of audible frequencies.

The unoccupied portion of the speech range, between frequencies 800 and 1500 cycles, is caused to-be occupied with noise currents. These may be supplied to circuit 6 by a variable frequenc oscillator W0. The element W0 may be 0 any conventional type of oscillator circuit in which the frequency of the wave produced is determined by the natural frequency of an electrical circuit comprised therein. A Hartley type of oscillator circuit such as is described in U. S. Patent to Hartley 1,356,753, issued October 26, 1920, is illustrated. The frequency of the oscillations supplied by W0 is made variable at an audible rate by including in the frequency determining circuit of the oscillator, a variable condenser driven. by a motor 8. The addition of the noise cur.- rents to the scrambled speech currents results effectively in a further distortion of till! speech currents. The resultant distorted speech currents are incapable of use in intelall ligent communication, unless special means complemental to those just described, are used to restore these currents to their initial condition.

The distorted speech currents are trans mitted through transformer 9 to vacuum tube speech amplifier WAS, which functions in the conventional manner. The amplified speech currents are impressed, through transformer 10, upon modulator W'M wherein they are combined with a high frequency.

\ euit comprising these condensers and inductance 15. The condensers 14 and 13 play no part in the operation of the oscillator, except to block the direct current supplied by the space current source 16, so as to confine currents from this source to the space path within the tube. These condensers are accordingly made to have large capacity as compared with that of condensers 11 and 12. This oscillator is coupled to the power amplifier by connecting together the filaments or cathodes and grids, respectively, of the two devices. The power am lifier can accordingly be considered as coup ed to the oscillator through the series combination of condensers 12 and 14.

The system of modulation employed is that commonly denominated constant current modulation, one exam le of which is illustrated and described in S. patent to Heising No. 1,442,147, January 16, 1923. The specific arrangement illustrated is a variation of that described in the above patent and is described in British Patent 168,056, August 31, 1922 to Heising. The plate circuits of the modulator and the power amplifier are supplied with space current from a direct current source 16, through a low frequency choke coil 17. The modulator is in effect a variable impedance device the function of which is to cause a. variable flow of current through the space path of the power amplifier WAP in response to and in accordance with impressed si a1 frequency variations, and accordingly, ecause of the resultant potential drop across the choke coil 17 to cause corresponding variations in the potential applied to the plate of the power amplifier. These low frequency variations in the plate potential of the power amplifier are effective to cause corresponding variations or modulations of theamplified carrier oscillations.

High frequency choke 18 revents the high frequency currents sup li by the oscillator W0 from flowing tirough the low frequency circuits The particular modulating arrangement shown difi'ers from that described in the above mentioned U. S. patent principally in that the low frequency variations are produced in the space potential of the power amplifier, instead of in the space potential of the oscillator. The arrangement is pre ferred in particularc'ascs, where it is desirable to maintain constancy of oscillation greater than can be secured by the means described in the U. S. patent in which the. oscillator oscillates directly into theantenna.

A feature of the circuit is the means for deriving negative fipotentials for the grids of the speech am 1i er WAS and the modulator VVM T e direct current source 16 which supplies space otential to the modulator and power amp ifier is used for this purpose. A resistance 19 is inserted between the negative terminal of this source and the cathodes of the modulator and speech amplifier. The rids of the two devices being connected at the junction point with this arrangement the space current flowing through the resistance 19 produces a drop of potential across the resistance whichis im ressed upon thegrids of the speech ampli er and modulator- This drop of potential will be substantially constant since on account of the type of modulation used, the current is 'substantiall r constant. In order to further insure an a sence of fluctuations in the current flowing through the resistance 19.11116 to the operation of the modulator, source 16 or other cause, a condenser 20 is con",

nected in shunt to the resistance. This'condenser is of low: impedance for current of the frequency of these fluctuations, and hence provides a shunt path through which they are diverted about the resistance 19. The use of the resistance and shunting condenser in this relation accordingly insures that a negative potential of constant value is impressed upon the grids of the amplifier and modulator, and thereby makes it unnecessary to use a separate source for this purpose. Obviously this expedient may be employed to supply hiasing potentials to any one or all of the discharge devices used in the system if found desirable.

Another feature of the above described system resides in the use of an over-size oscillator W0 Its use results in a reduction of'the reaction on the oscillator ofthe power amplifier on account ofthe shunting effect of certain of the amplifier tube impedances. An over-size oscillator is distinguished from a normal size oscillator by a design which results in a greater amplitude of current in its output circuit than would be required by its normal operation in the system. lVith the larger amplitude of current sufiicient voltage for exciting the grid of the power amplifier can be obtained by using a larger coupling capacity supplied by condensers 12 and 14, than would be necessary if a smaller size oscillator were used. The grid-filament and grid-plate resistance and capacity of the power amplifier have a much smaller effect on the frequency of the oscillator because of the small reactance that would be parallelled. This results in a greater constancy of frequency in the oscil lator, and, therefore, in the system as a whole. This expedient is of value, for example, where it is desired to simplify the transmitting circuits as by substituting a single stage for a multi-stage power amplifier. A simplification of this kind tends to result in greater frequency variations in the system. Since simplification of this particular kind means a reduction in the power of the set the expedient is useful in securing substantially as great a constancy of frequency in small power transmitting sets as can be achieved by other means in large power sets. Because of the economy of space and power there required this expedient is especially applicable on board ship as in Fig. 2, in the system of which as well as in that of Fig. 1, this expedient maybe used. In a typical instance the use of this expedient made possible the use of only four tubes of only two sizes a four watt speech amplifier tube and two hundred and fifty watt modulator, oscillator and power amplifier tubes.

The modulated wave radiated from the station of Fig. 1 is received by the antenna A N of Fig. 2, which is tuned broadly to the carrier frequency. This wave is selected by av selective means FH, which may take the form of a high frequency band pass filter. or tuned circuit, and is detected in device ED. This device may be a vacuum tube or any other type of device capable of demodulating the received modulated wave.

The wave resulting from detection is identical with the distorted low frequency wave supplied to the transformer 9 of Fig. 1. The scrambled speech currents of this wave to the exclusion of the noise currents are selected by filter circuits EFB and EFB,. The former EFB selects the sub-band 1ying between 200 and 800 cycles and 1500 and 2500 cycles. The latter EFB selects the sub-band between 2700 and 3400 cycles. These filters are similar in function to filters \VFB and VFB respectively of Fig. 1 and may be similar in construction.

The frequencies selected by filter EFB are transmitted unchanged through circuit 21, to receiver R. Currents selected by filter EFB are shifted back to the position in the frequency spectrum that they initially occupied, that is, to 800 to 1500 cycles. This is accomplished b modulator EM oscillator E0 and ban pass filter EFB according to a method analogous to that occurring in branch circuit 5 of Fig. 1. The resultant sub-band is impressed on the receiver R. The superposed sub-bands impressed on this receiver, constitute a band which is identical with that supplied to the circuit 2 of Fig. 1.

There has accordingly been provided, in the transmission channel above described, means whereby a casual or unauthorized operator can intercept and reproduce the transmitted messages only with great difliculty, whereas the desired receiving station is equipped with special means insuring efficient reception of such signals. An interceptor in order to achieve any substantial degree of success in reading the signal mes sageswould have to be equipped with unscrambling means substantially identical with those above described.

The operation in transmission westward is similar to the eastward transmission above described, except as affected by the fact that transmission is from ship to shore instead of from shore to ship. The elements E0, EFB, EAS, EM E0 and EAP function similarly to the elements WO. WFB, WAS, WM WVO and WAP of Fig. 1. The apparatus indicated by block EST is a speech transposing arrangement similar to that included in branch 5 of Fi 1. The modulated Wave in the output circuit of the power amplifier EAP is impressed through transformer 22, an antenna AN which functions both as a transmitting and a receiving antenna. The relation of the parts of the antenna circuit whereby it may operate efficiently for transmitting and re-- ceiving is described in Canadian Patent 232.492, July 3, 1923, to Heising.

The waves transmitted from antenna AN of Fig. 2 are received by antenna AN of Fig. 1. Since this figure illustrates a shore station, it is convenient to use separate antennae for transmitting and receiving. By properly relating the antennae geographically or geometrically interference and singing at that station can largely be avoided. Although a method of reception similar to that of Fig. 2 may be used at the shore station. the alternative method illustrated in Fig. 1 can equally well be used and perhaps provides a more selective arrangement for distinguishing between desired and undesired incoming waves. The waves received by antenna AN, are combined, with oscillations supplied by a local source W0 in high frequency detector or demodulator \VDH. This detector functions as a frequenc combining device to produce a wave of intermediate frequency, equal to the freby device VVAS The rectangle WST represents a speech transposing arrangement which corresponds to EST of Fig. 2. WST comprises elements which cooperate in the same manner as the element EFB EM E0 and EFB of Fig. 2. The band pass filter WFB functions in a manner similar to filter EFB of Fig. 2. The circuits comprising the two branches including devices VVlE B and VVST accordingly together constitute a speech unscrambling circuit. The reorganized speech wave resulting from the unscrambling operation are impressed through hybrid coil 3 on low frequency line 1.

It will be obvious that the general principles herein disclosed may be embodied in many organizations widely difi'erent than those illustrated without departing from the spirit of the invention- Accordingly, it is to be undersfood that this invention is not limited to the arrangements or specific details disclosed but only by the scope of the appended claims.

What isclaimed is:

1. A source of oscillations comprising an evacuated vessel containing a cathode, an anode and a third electrode, and an oscillation circuit havin a capacitatively reactive path between sai third electrode and said cathode and a separate capacitatively reactive path between said anode and said cathode; an electric discharge repeating device comprising at least two electrodes; means connecting said two electrodes to one of the pairs of electrodes of said source between which there is a capacitatively reactive path; said source belng designed to produce an energy output greater than would be required for eflicient amplification of said output by said repeating device.

2. The combination specified in claim 1 in which the power output of the source is substantially equal to the normal power output of the device.

3. In combination, an electric discharge repeating device comprising at least two electrodes, an electric discharge oscillation source, and capacitative coupling means between said source and said electrodes, said means also comprising a portion of the frequency determining circuit of said source, the capacitative reactance of said means being made small as compared with the impedance of said device between said electrodes, and said source being designed to produce a sufficiently large output current that the current flow in said means, with the value of the capacity reactance, provides an eflicient coupling between the source and device for distortionless repeating of the oscillations generated by said source. 7

4. In combination, an electric discharge repeating device comprising .at least two electrodes, an electric discharge oscillation source, and capacitive coupling means between said source and said electrodes, the capacity reactance of said means being made small as compared with the im ed'ance of said device between said electro es, and said source'being designed to produce sufliciently large output energy that the current flow 1n said means, with the value of the capacity reactance, provides the proper potential for distortionless repeating of the oscillations generated by said source.

5. In combination, an electric discharge repeating device comprising at least two electrodes, an electric discharge oscillation source, and capacitive coupling means between said source and said electrodes, said means also comprising a portion of the frequency determining circuit of said source, said means taken in connection with the proportions of the various elements of the source being such that the source produces wattless energy which is large as compared with the wattless energy flowing between said two electrodes of the repeating device.

In witness whereof, I hereunto subscribe my name this 26th day of November, A. D.,

RAYMOND A. HEISING. 

